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Final destination: Ma’at region

The decision has been made for the location of Rosetta’s controlled impact on Comet 67P/Churyumov-Gerasimenko on 30 September 2016, ending the mission.

The spacecraft will target Ma’at, a region hosting some active pits on the small comet lobe. This region has been chosen for its scientific potential and taking into account key operational constraints involved in executing the descent.

The expected time for Rosetta’s contact with the surface of the comet is approximately 12:30 CEST / 10:30 UTC. More details on the timeline and likely data to be taken during the descent will follow shortly.

Discussion: 20 comments

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loganPosted on 21/07/2016 at 19:46

.Quite probably the final path is also decided, then. Have the feeling that [is] still within [financial] limits a stand-by [scientific] salute at Coraline’s Next Visit. She will be passing by our neighborhood. Little fuel, high tech. 🙂

Looks like an interesting place to head towards as a final resting place. Plenty of pits to get a close look at.

On a less serious note; was the decision made by Ma’at Taylor, by any chance? Sorry, I’ll get my coat…..

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KamalPosted on 06/08/2016 at 07:55

IanW16: And if it bounces it might fall all the way to the bigger lobe.

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GeraldPosted on 22/07/2016 at 15:54

the result of Ma’-thema-tical trajectory calculations.

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loganPosted on 08/09/2016 at 15:32

“Ma’-thema” Looks a fine place, to come down for a rest.

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Cesare Guaita (GAT/Milano PlanetariumPosted on 23/07/2016 at 17:36

The weight of Rosetta over the comet will be about 300 g. What’s the possibility that the Orbiter could jump as Philae ?
If so, instruments on board should have time to make (and to send to Earth !) chemical analyses on the (organic) powder that will be raised.
In other word : have the team take in account this possibility even to study a road that could favor it ?
Thanks a lot for a reply !

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HarveyPosted on 25/07/2016 at 19:37

The high gain antenna and solar panels are extremely unlikely to survive the impact. The very best possibility is the low data rate, low gain antenna and residual battery power.
Virtually no chance of anything useful post impact in afraid.

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Marco ParigiPosted on 27/07/2016 at 00:42

Hi Harvey,

All the more reason not to impact in the first place, if science is the most important objective. If theatrics, politics or psychology are more important, *then* I definitely can see why impacting is a better option. For the scientific value, I am afraid I cannot.

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HarveyPosted on 29/07/2016 at 17:07

As I’ve said before , I don’t think the decision has been particularly well explained.
However the team is in possession of far better information on the spacecrafts health and resources than we are. They will also have a huge interest in extracting the last gasp of science from it. I very much doubt ‘theatrics’ or even politics will have had much input into the decision; scientific and engineering teams don’t work like that. Money certainly will, and the need for people and resources to move on to other things which are more productive.
So whilst I do think it could be better explained, I’m prepared to accept this superb team knows what it is doing.

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Marco ParigiPosted on 01/08/2016 at 11:20

I really do not see that any engineering information in their possession changes the calculus of the decision making process. There is no differential in cost in abandoning Rosetta in a hibernated state or in an impacted state.

There are potential opportunities in the future. We could change our mind and re-activate the mission Hitomi style if there is a greater than zero chance of wake up in 3 years.

Yes. I would like an explanation of how an impact benefits science over a “near miss”

I don’t see it as an engineering or science decision, but simple strategic discretion. For posterity, physically knowing that Rosetta is somewhere on the nucleus is perceived as more of a gift to the future than a forever lost craft in space.

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Marco ParigiPosted on 01/08/2016 at 11:25

That should be Akatsuki style “I’ll be Back!”

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Peter ElbroPosted on 27/07/2016 at 09:45

Even though the weight on the comment may only be about 300g the mass is still about 2,300 kg and a collision with the comet will undoubtedly cause a lot of damage as the orbiter has no energy absorbing landing system. If it survives the impact and it is still working the high-gain antenna is unlikely to be aligned with Earth any more so sending back a lot of data will not be possible.but it may be possible to send back a very limited amount of information through its low-gain command antennas. We will have to wait and see.

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loganPosted on 23/07/2016 at 23:04

Considering how low are the magnetic readings of the core. Couldn’t the magnetometer output be introduced to the attitude loop?

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HarveyPosted on 29/07/2016 at 17:09

Up till impact, you can orientate in the normal way. The magnetometers are on booms, and unlikely to survive impact.

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loganPosted on 26/07/2016 at 18:45

Those boulders at bottom right suggest to be the remains of a former [higher] surface:

The left hand outline of your boulders describes the same shape of the Seth rim a few hundred metres away (as do all the boulders forming that long meandering line along Hapi). They exhibit translational symmetry.

Your boulders, referred to in your linked picture are the same as the ones at bottom of the right hand red line in the header.

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ianw16Posted on 29/07/2016 at 17:03

Or the cliff has retreated, as seen at Tempel 1, thus leaving behind a record of where it retreated from. I’d also have to be convinced that they aren’t recent falls (if that’s what they are), and have just followed the terrain into the local gravitational low.

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A. CooperPosted on 09/08/2016 at 15:41

ianw16

Late reply (only just seen your comment). The faithfulness of the match between the boulder line and cliff 300-400 metres away is simply to faithful to be attributable to cliff retreat via erosion or rock fall following the gravity vector.

Erosion would involve at least some randomness in terms of sublimation rates and lead to evolution in the line of the cliff during retreat. This would probably occur due to the complex variations in shadowing at Hapi during the daily (sometimes twice daily) illumination cycle. And the non-homogeneity of the matrix (inherent cracks, porosity variations) would ensure different rates of sublimation along the cliff edge too. Both processes would lead to cliff line evolution.

Vincent et al 2015 expressed doubts that a boulder line just 150 metres or so from the base of the Aswan rim cliff could be due to boulders falling and rolling to that distance. Those too show an even more remarkable affinity with the cliff Aswan cliff base. Even if it were due to boulders falling and rolling, can one really explain the fact that every one rolls an identical 150 metres +/- 5 metres and does so at an exact perpendicular vector to the average cliff line? Firstly, they’d get kicked in random directions as they bumped down the cliff face before rolling. That means that even if they did all roll the same distance, they’d not come to rest along a faithfully translated cliff line. Secondly, there’s the volume:surface area issue of different size boulders affecting the KE: friction attenuation. That too would affect the final line.

If they’re following the gravity vector then that’s what they’ll follow. The gravity vector isn’t a proxy for cliff edge shape memory, it has its own characteristic vagaries. If the boulders really did roll from the Seth cliff to where they are, they would be subject to coming to rest where the local gravity vector could no longer overcome shear resistance (see Groussin et al. 2015’s work on strengths and slopes using boulder shear resistance to rolling). The line of the cusp of this complex relationship, sitting 300-400 metres from the Seth cliff rim isn’t going to have any memory of the shape of that cliff rim. It may have the very vaguest memory in terms of the average line being parallel but not with all the very sharp twists and turns being faithful to the 10-20 metre scale over 300-400 metres. And then there’s the volume surface area issue and the cliff-bouncing angled vector, Vincent et al’s crumbling, identical distances rolled after dropping from different heights. Not to mention simply having enough KE to roll that far in the first place (another Vincent et al. objection. The list of objections to rolling goes on and on.

As for erosion, maintaining a matching perimeter, how far do we erode it back before it really is rather a surprise that the matches are so faithful? Vincent et al’s 150 m or Hapi’s 300-400 m or Imhotep’s 750 m? See the ‘red’ slide, part 43 on the stretch blog. That’s not a boulder line match, rather, a cliff perimeter match with an exquisitely faithful meandering line. The point is, it can’t be explained via erosion.